The invention relates to a method for establishing a data communication connection in a data channel where PAM signals are utilized, the transmitter transmitting a training sequence, formed of predetermined symbols, a predetermined number of times, in which method: the data channel is monitored in order to detect a predetermined signal, samples are taken from the data channel, and the amplification of the receiver is adjusted in such a way that the received signals settle at a predetermined level.
The invention relates especially to multipoint modem networks utilizing PAM (Pulse Amplitude Modulation) signals and comprising one master modem which transmits the same data to several slave modems. The slave modems alternately transmit data to the master modem by reserving the channel in turn for their own use. In addition to transmission rate, training time also significantly affects the amount of data that can be transmitted in a time unit in such a network. In this connection, training time refers to the time required for establishing a connection. During the training time, synchronization is performed with the remote clock, and a descrambler and amplification are set, among other things.
In a previously known arrangement for establishing a datacommunication connection, fixed correction coefficients, dependent on the data channel used, are determined beforehand for the receiver, and, by means of the coefficients, the interference resulting from the data channel, between the symbols to be transmitted, is compensated for. A typical known equalizer of this type is a FIR (Finite Impulse Response) equalizer by means of which both the front part and the tail part can be removed from a pulse response. Since the correction coefficients are fixed, a connection can be established by setting correct amplification, synchronizing the receiver with the transmitter clock, and by setting a descrambler.
The major drawback of the aforementioned known solution is that when it is applied, the pulse response of the data channel must be known, so that the fixed correction coefficients can be set correctly. For example, when a multipoint network is set up, the assembler must manually adjust the correction coefficients of each modem to a suitable value. This is due to the fact that, for example when a copper cable is used, the pulse response of the data channel changes according to the cable length, so that the correction coefficients must always be set specifically for each case.